Pressure-sensitive adhesive layer-forming organopolysiloxane composition, and use thereof

ABSTRACT

Provided is a curing reactive organopolysiloxane composition that forms a pressure-sensitive adhesive layer having excellent curing properties, a wide range of designable viscoelastic properties such as storage elastic modulus (G′) and the like, and practically sufficient pressure-sensitive adhesive strength and tensile adhesive strength. The organopolysiloxane composition comprises: (A) an organopolysiloxane having an alkenyl group; (B) an organopolysiloxane resin with 9 mol % or less of hydroxyl groups or the like relative to all silicon atoms in a molecule or resin mixture thereof; (C) an organohydrogenpolysiloxane; (D) an organic silicon compound having an alkenyl group; and (E) a hydrosilylation reaction catalyst. A ratio (molar ratio) of the substance amount of SiH groups in component (C) relative to the sum of alkenyl groups in components (A), (B) and (D) is 1.0 or less.

TECHNICAL FIELD

The present invention relates to a curing reactive organopolysiloxane composition that forms a pressure-sensitive adhesive layer and an application thereof.

BACKGROUND ART

Polysiloxane-based pressure-sensitive adhesive compositions are superior to acrylic-based and rubber-based pressure-sensitive adhesive compositions in electrical insulation, heat resistance, cold resistance, pressure-sensitive adhesion to various adherends, and transparency if necessary, and therefore, the addition reaction curing type pressure-sensitive adhesive compositions in particular are widely used. Furthermore, in recent years, applications to advanced electronics materials such as smart devices and the like, display element fields, speakers, and the like are being considered, and polysiloxane-based pressure-sensitive adhesives with excellent heat and cold resistance are expected to effectively function to protect electrode layers and display layers and improve adhesion between layers.

In particular, in recent material development, there is a need for polysiloxane-based pressure-sensitive adhesive composition with a high degree of freedom in the design of the storage elastic modulus (for example, shear storage elastic modulus G′), excellent curability, and sufficient pressure-sensitive adhesive strength for practical use, in a wide temperature range including a room temperature. However, the pressure-sensitive adhesive composition described in the known literature and the like do not sufficiently satisfy these properties, and there is still room for improvement.

For example, while Patent Document 1 discloses an adhesive rubber sheet, there is no mention or suggestion of using a combination of resin components having less resin component content in the ratio of the resin component and siloxane polymer component in addition to having certain characteristics such as molecular weight and hydroxyl group content. Further, the adhesive rubber sheet uses finely powdered silica and the like and does not satisfy the intended storage elastic modulus (G′) of the present invention.

Similarly, while Patent Document 2 discloses a silicone pressure-sensitive adhesive which uses an organopolysiloxane resin having a number average molecular weight of 950 to 1600, there is no mention or suggestion of using a combination of resin components with specific characteristics such as a content of hydroxyl groups. Further, while the silicone pressure-sensitive adhesive has a certain adhesive force, it does not satisfy the intended storage elastic modulus (G′) of the present invention.

In contrast, Patent Document 3 proposes a laminated body provided with a transparent resin adhesive layer, wherein the substance amount ratio of the resin component to the polymer component is within a range of 0.5 to 1.0 and the difference in the storage elastic modulus G′ at low temperatures and room temperature is small.

Unfortunately, only a condensation reactive transparent resin adhesive layer is specifically disclosed, making the curing reaction problematically too slow for industrial use. Further, the transparent resin adhesive layer does not satisfy the intended storage elastic modulus (G′) and sufficient adhesion for practical use according to the present invention.

Here, the present applicants propose a curable silicone composition capable of forming a cured layer having a sufficient elastic modulus and loss coefficient (tan δ) in a flexible laminated body application in Patent Document 4. Unfortunately, while the composition specifically disclosed in the examples and the like partially discloses a combination of resin components having different weight average molecular weights, it cannot sufficiently solve the problems of the present invention.

Note that although these prior art documents describe the use of an adhesion promoter as an optional component, there is no description or suggestion of the use of an organic silicon compound adhesion promoter having a specific functional group in a specific quantitative range in relation to a crosslinking agent, and technical effects as a result thereof.

PRIOR ART DOCUMENTS Patent Documents

-   Patent Document 1: Japanese Patent Application Publication No.     2006-225420 A -   Patent Document 2: Japanese Patent Application Publication No.     H05-214316 A -   Patent Document 3: WO 2017/082654 A1 -   Patent Document 4: WO 2017/188308 A1

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

In order to solve the aforementioned problems, an object of the present invention is to provide a curing reactive organopolysiloxane composition that forms a pressure-sensitive adhesive layer having a high degree of freedom in the design of the storage elastic modulus (G′), excellent curability, and a practically sufficient pressure-sensitive adhesive strength. Another object of the present invention is to provide a use of the curing reactive organopolysiloxane composition or a cured product thereof as a pressure-sensitive adhesive layer, a use of the same as an elastic pressure-sensitive adhesive member in various applications, and an apparatus or device provided therewith.

Means for Solving the Problems

As a result of conducting diligent research on the problems described above, the present inventors arrived at the present invention. In other words, one object of the present invention is achieved by using, in a hydrosilylation reaction curing organopolysiloxane composition for forming a pressure-sensitive adhesive layer, an organopolysiloxane resin, in which the sum of the contents of hydroxyl groups and hydrolyzable groups relative to all silicon atoms in a molecule is 9 mol % or less, and using an organic silicon compound containing an alkenyl group in a molecule and having properties that can be used as an adhesion promoter (these are components that do not correspond to alkenyl group-containing dialkylpolysiloxanes or alkenyl group-containing organopolysiloxane resins used as a main agent of ordinary silicone pressure-sensitive adhesives). Furthermore, the aforementioned problem may be resolved by a use of the curing reactive organopolysiloxane composition or a cured product thereof as a pressure-sensitive adhesive layer, use of the same an electronic material or display device member, and an electronic component, display device, or speaker provided therewith.

Effects of the Invention

The organopolysiloxane composition for forming a pressure-sensitive adhesive layer of the present invention has excellent curability due to a hydrosilylation reaction, and can cure to form a pressure-sensitive adhesive layer having practically sufficient adhesive strength, and particularly having excellent tensile adhesive strength, a high degree of freedom in the design of the storage elastic modulus (G′), and practically sufficient adhesion. Furthermore, the curing reactive organopolysiloxane composition or a cured product thereof can be suitably used as a pressure-sensitive adhesive layer, electronic material, or a display device member. An electrical or electronic component or display device provided therewith satisfies the aforementioned required properties, solves problems with curing failures, and has sufficient viscoelasticity of an adhesive layer in a wide temperature region including low temperatures. Therefore, a pressure-sensitive adhesive layer can be formed in which a problem with failures of close fitting properties to a substrate of an electronic component and the like in a temperature region including low temperatures to room temperature is unlikely to occur. Thus, there is an advantage where industrialization can be expected to be simple, and improvements in the performance of a laminated body of an obtained display device, speaker, or the like can be expected.

MODE FOR CARRYING OUT THE INVENTION

[Organopolysiloxane Composition for Forming a Pressure-Sensitive Adhesive Layer]

First, the organopolysiloxane composition for forming a pressure-sensitive adhesive layer according to the present invention will be described. The composition quickly cures by a curing reaction including a hydrosilylation reaction to form a pressure-sensitive adhesive layer having a high degree of freedom of the design of the storage elastic modulus (G′), preferably allows the elastic modulus to be designed in a wide range where the shear storage elastic modulus G′ at room temperature is 0.005 MPa or more, and having practically sufficient adhesive strength and excellent tensile adhesive strength. Hereinafter, each of the components thereof, quantitative ranges thereof, and properties of the pressure-sensitive adhesive layer will be described below.

As described above, the organopolysiloxane composition of the present invention cures via a hydrosilylation reaction so as to form a pressure-sensitive adhesive layer having a certain pressure-sensitive adhesive strength. The composition uses an organopolysiloxane resin in which the sum of the contents of hydroxyl groups and hydrolyzable groups relative to all silicon atoms in the molecule is 9 mol % or less, and uses an organic silicon compound having at least one alkenyl group in a molecule, which does not correspond to a chain or cyclic organopolysiloxane or organopolysiloxane resin having an alkenyl group serving as a main agent. The SiH/Vi ratio in the composition is designed to be 1.0 or more.

Normally, a hydrosilylation reaction curing silicone pressure-sensitive adhesive uses a chain or cyclic polydialkylsiloxane having an alkenyl group in a molecule as a main agent and an organopolysiloxane resin as an adhesion imparting component to achieve pressure-sensitive adhesiveness and pressure-sensitive adhesive properties of a cured product. However, in the present invention, a specific amount of an organic silicon compound having an alkenyl group that does not correspond to a main agent or adhesion imparting component is used, such that the curability of the composition is improved, the shear storage elastic modulus G′, stress at 500% strain, and pressure-sensitive adhesive strength of an obtained pressure-sensitive adhesive layer can be controlled within a practical range with an extremely high degree of freedom, and the tensile strength and the like of the obtained pressure-sensitive adhesive layer can be further improved.

Specifically, the organopolysiloxane composition of the present invention contains:

(A) a chain or cyclic organopolysiloxane having on average more than one alkenyl group in a molecule; (B) an organopolysiloxane resin in which the sum of the contents of hydroxyl groups and hydrolyzable groups relative to all silicon atoms in a molecule is 9 mol % or less; (C) an organohydrogenpolysiloxane having at least two Si—H bonds in a molecule; (D) an organic silicon compound having on average more than one alkenyl group in a molecule (excluding components corresponding to components (A) and (B)); (E) an effective amount of a hydrosilylation reaction catalyst; and optionally, (A′) a chain organopolysiloxane not containing a reactive group containing a carbon-carbon double bond in a molecule; wherein an amount of component (C) is an amount such that the ratio (molar ratio) of the substance amount of SiH groups in component (C) to the total substance amount of the alkenyl groups in components (A), (B), and (D) is 1.0 or more. Furthermore, the composition contains a hydrosilylation reaction catalyst. Therefore, the composition may further contain (F) a curing retarder from the perspective of handling workability, and may further contain another additive within a scope that does not contradict the object of the present invention. Hereinafter, each component will be described.

The alkenyl group-containing organopolysiloxane for component (A) is a chain or cyclic polysiloxane molecule, is the main agent (base polymer) of the composition, and contains on average more than one alkenyl group bonded to silicon atom in a molecule, where the preferred number of alkenyl groups is 1.5 or more in a molecule. Examples of the alkenyl groups of the organopolysiloxane for component (A) include alkenyl groups having a carbon number of from 2 to 10 such as vinyl groups, allyl groups, butenyl groups, pentenyl groups, hexenyl groups, and heptenyl groups, with vinyl groups or hexenyl groups being particularly preferable. Examples of the bonding position of the alkenyl groups in component (A) include the molecular chain terminals and/or the molecular side chains. Note that component (A) may contain a single component or may be a mixture of two or more different components.

In the organopolysiloxane for component (A), examples of organic groups bonded to silicon atoms other than alkenyl groups include: methyl groups and other alkyl groups; aralkyl groups; alkyl halide groups; and the like. Methyl groups and phenyl groups are particularly preferred.

Component (A) is different from component (B) and has a chain or cyclic polysiloxane molecular structure. For example, component (A) is preferably a straight chain, partially branched straight chain (branched chain), or cyclic, and may partially include a cyclic or three-dimensional network. Suitably, a straight chain or branched-chain diorganopolysiloxane in which a main chain contains repeating diorganosiloxane units and both ends of a molecular chain are blocked with triorganosiloxy groups is preferable. Polydialkylsiloxanes having an alkenyl group in a molecule and copolymers of polydialkylsiloxane and arylalkylsiloxane are industrially common forms. Note that the siloxane units which provide a branched-chain organopolysiloxane are T units or Q units described below.

The properties of component (A) at room temperature may be those of an oily or raw rubber-like substance, with a viscosity of component (A) being no lower than 50 mPa·s and particularly preferably no lower than 100 mPa·s at 25° C. In particular, when the organopolysiloxane composition according to the present invention is a solvent type, at least a portion of component (A) is (A1) a raw rubber-like alkenyl group-containing organopolysiloxane having a viscosity of no less than 100,000 mPa·s at 25° C. or having a plasticity (the thickness when a 1 kgf load applied for 3 minutes to a 4.2 g spherical sample at 25° C. was read up to 1/100 mm and this value was multiplied by 100) within a range of from 50 to 200, more preferably within a range of from 80 to 180 as measured in accordance with the method as prescribed in JIS K6249.

Note that from the perspective of preventing contact failure and the like, these alkenyl group-containing organopolysiloxanes preferably have a volatile or low molecular weight siloxane oligomer (octamethyltetrasiloxane (D4), decamethylpentasiloxane (D5), or the like) reduced or eliminated. While the degree can be designed as desired, it may be less than 1% by mass of the total component (A), less than 0.1% by mass for each siloxane oligomer, and may be reduced to the vicinity of the detection limit as required.

Although the amount of alkenyl groups in component (A1) is not particularly limited, from the perspective of the technical effects of the present invention, the content of the vinyl (CH₂═CH) portions in the alkenyl groups in component (A1) (hereinafter, referred to as the “content of vinyl”) is preferably within a range of 0.005 to 0.400 mass %, and particularly preferably within a range of 0.005 to 0.300 mass %. Furthermore, from the perspective of increasing the elastic modulus and tensile stress of the obtained pressure-sensitive adhesive layer, the content of vinyl described above is more preferably within a range of 0.03 to 0.40 mass %, and particularly preferably within a range of 0.04 to 0.40 mass %. Component (A) may be a mixture of two types of alkenyl group-containing organopolysiloxanes having different amounts of vinyl, but the average value of the vinyl amount thereof is preferably within the aforementioned range.

Even component (A) having a lower viscosity than the abovementioned component (A1) is available as component (A) of the present invention. Specifically, an organopolysiloxane (A2) containing alkenyl groups having a viscosity of less than 100,000 mPa·s at 25° C. is available. Here, examples other than the viscosity of component (A2) are the same as component (A1).

In terms of the technical effects of the present invention, 50 mass % or more of component (A) is preferably an alkenyl group-containing organopolysiloxane with a high degree of polymerization, which is component (A1), with 75 to 100 mass % thereof particularly preferably component (A1). That is, when component (A1) (=an alkenyl group-containing organopolysiloxane with a higher degree of polymerization) and component (A2) (=an alkenyl group-containing organopolysiloxane with a lower degree of polymerization) are used in combination as component (A) of the present invention, the mass ratios of both thereof range from 50:50 to 100:0, more suitably 75:25 to 100:0 or 75:25 to 90:10.

As described above, component (A) may be a cyclic alkenyl group-containing organopolysiloxane, and specifically may be a cyclic siloxane having an alkenyl group such as 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane or the like. From the perspective of the technical effects of the present invention, component (A) preferably contains a chain alkenyl group-containing organopolysiloxane. The cyclic alkenyl group-containing organopolysiloxane may have a function as a reactive diluent or a control agent of curing reactivity in addition to a function as a main agent, and is preferably appropriately used as necessary based on the viscosity of the composition to be designed, the manufacturing method, curing properties, and the like.

The organopolysiloxane resin (B) is a characteristic configuration of the present invention, is a pressure-sensitive adhesion imparting component that imparts pressure-sensitive adhesion to a substrate, and is also a component that achieves a storage elastic modulus and practical pressure-sensitive adhesive strength range. More specifically, component (B) is an organopolysiloxane resin or mixture thereof, where the content of hydroxyl groups or hydrolyzable groups is suppressed, and where a hydrolysis/polymerization reaction between components (B) tends not to occur, with the combined use of resins of different average molecular weights achieving a predetermined storage elastic modulus and practical pressure-sensitive adhesive strength range in the pressure-sensitive adhesive layer, which is a cured product thereof.

Specifically, in component (B), the sum of the contents of hydroxyl groups and hydrolyzable groups in a molecule is within a range of 9 mol % or less relative to all silicon atoms in the organopolysiloxane resin molecule, and preferably 7 mol % or less relative to all silicon atoms in the molecule. Note that in component (B), the contents of such hydroxyl groups and hydrolyzable groups can be expressed by converting all of these functional groups into hydroxyl groups. In this case, when the mass % is calculated assuming that all of the hydrolyzable groups other than the hydroxyl groups in the organopolysiloxane resin molecule are hydroxyl groups (OH), the sum of the contents of the aforementioned hydroxyl groups and hydrolyzable groups can be expressed such that the contents of these hydrolyzable groups which are converted into hydroxyl groups and hydroxyl groups in the organopolysiloxane resin molecule is 2.0 mass % or less, and preferably 1.6 mass % or less. The hydroxyl groups or hydrolysable groups are groups which are directly bonded to silicon of the T units or Q units, and the like among the siloxane units in the below-mentioned resin structure, and obtained by hydrolyzing the silane or silane derivative which is the raw material. Consequently, the content of hydroxyl groups or hydrolyzable groups can be reduced by hydrolyzing the synthesized organopolysiloxane resin with a silylating agent such as trimethylsilane.

In component (B), when the content of the hydroxyl groups or hydrolyzable groups exceeds the aforementioned upper limit, a condensation reaction between organopolysiloxane resin molecules proceeds, thereby facilitating the formation of an organopolysiloxane resin structure having a large molecular weight in a cured product. Such an organopolysiloxane resin having a high molecular weight tends to impair the curability of the overall composition, the curability of the composition at low temperatures may be insufficient, and the resulting pressure-sensitive adhesive layer may not have sufficient storage elastic modulus for practical use. Furthermore, a large content of unreacted hydroxyl groups or hydrolyzable groups being present in component (B) may cause curing defects by inhibiting a hydrosilylation reaction, or the temperature conditions required for the advancement of a curing reaction may be high, which may be not preferred in industrial production.

Component (B) is an organopolysiloxane resin or a mixture thereof and is an organopolysiloxane having a three-dimensional structure. Examples include: resins containing an R₂SiO_(2/2) unit (D unit) and RSiO_(3/2) unit (T unit) (where R mutually independently represents a monovalent organic group) and having a content of hydroxyl groups or hydrolyzable groups within the aforementioned range; resins containing only a T unit and having a content of hydroxyl groups or hydrolyzable groups within the aforementioned range; resins containing an R₃SiO_(1/2) unit (M unit) and SiO_(4/2) unit (Q unit) and having a content of hydroxyl groups or hydrolyzable groups within the aforementioned range; and the like. In particular, a resin (also referred to as MQ resin) is preferably used, which contains an R₃SiO_(1/2) unit (M unit) and SiO_(4/2) unit (Q unit) and where the sum of the contents of hydroxyl groups and hydrolyzable groups with regard to all silicon atoms in the molecule is 0 to 7 mol % (and preferably within a range of 0.0 to 1.6 mass % when all of these functional groups are converted into hydroxyl groups).

The monovalent organic group of R is preferably a monovalent hydrocarbon group having a carbon number of from 1 to 10, with examples thereof including alkyl groups having a carbon number of from 1 to 10, alkenyl groups having a carbon number of from 2 to 10, aryl groups having a carbon number of from 6 to 10, cycloalkyl groups having a carbon number of from 6 to 10, benzyl groups, phenylethyl groups, and phenylpropyl groups. In particular, 90 mole % or more of R is preferably alkyl groups having 1 to 6 carbon atoms or phenyl groups, while 95 to 100 mole % of R is particularly preferably methyl groups or phenyl groups.

When component (B) is a resin containing an R₃SiO_(1/2) unit (M unit) and SiO_(4/2) unit (Q unit), the molar ratio of M units to Q units is preferably from 0.5 to 2.0. This is because when the molar ratio is less than 0.5, the adhesive force to the substrate may be diminished, whereas when the molar ratio is greater than 2.0, the cohesive strength of the material constituting the adhesive layer decreases. Moreover, D units and T units may also be included in component (B) to an extent that does not impair the characteristics of the present invention. Further, in order to prevent contact failure and the like, these organopolysiloxane resins may have a low molecular weight siloxane oligomer reduced or eliminated.

Preferably, component (B) in the present invention is an organopolysiloxane resin mixture containing the following component (b1) and component (b2) at a mass ratio of 1:99 to 99:1:

(b1) an organopolysiloxane resin, wherein the total content of hydroxyl groups and hydrolyzable groups relative to all silicon atoms in the molecule is 9 mole % or less, and a weight average molecular weight (Mw) measured in terms of standard polystyrene by gel permeation chromatography (GPC) is 4500 or more; and (b2) an organopolysiloxane resin, wherein the total content of hydroxyl groups and hydrolyzable groups relative to all silicon atoms in the molecule is 9 mole % or less, and a weight average molecular weight (Mw) measured in terms of standard polystyrene by gel permeation chromatography (GPC) is less than 4500;

The organopolysiloxane resins which are components (b1) and (b2) differ from each other in terms of the weight average molecular weight (Mw) thereof. Here, the weight average molecular weight (Mw) is the average molecular weight, taking into consideration the proportion of each molecule in each organopolysiloxane resin measured in terms of standard polystyrene by gel permeation chromatography (GPC).

Component (b1) is an organopolysiloxane resin having a large molecular weight, wherein the weight average molecular weight (Mw) thereof is 4500 or more, preferably 5000 or more, and particularly preferably 5500 or more. In practical use, component (b1) is particularly suitably a resin containing the aforementioned R₃SiO_(1/2) unit (M unit) and SiO_(4/2) unit (Q unit), where the weight average molecular weight (Mw) is within a range of 5000 to 10000.

Component (b2) is an organopolysiloxane resin having a small molecular weight, wherein the weight average molecular weight (Mw) thereof is less than 4500, preferably 4000 or less, and particularly preferably 3750 or less. In practical use, component (b1) is particularly suitably a resin containing the aforementioned R₃SiO_(1/2) unit (M unit) and SiO_(4/2) unit (Q unit), where the weight average molecular weight (Mw) is within a range of 500 to 3750.

If component (B) is an organopolysiloxane resin mixture containing the aforementioned component (b1) and component (b2) at a mass ratio of 1:99 to 99:1, while not particularly limited thereto, the mixing ratio thereof may be within a range of 5:95 to 95:5, within a range of 10:90 to 90:10, or within a range of 15:85 to 85:15.

[Mass Ratio of Component (B) to Components (A) and (A′)]

The organopolysiloxane composition for forming a pressure-sensitive adhesive layer according to the present invention characteristically preferably have a mass ratio of component (B), which is an organopolysiloxane resin, to component (A) and component (A′) described later, which are chain or cyclic reactive siloxane components, within a range of 0.9 to 3.0. In particular, this is because, when the abovementioned characteristic organopolysiloxane resin mixture is selected as component (B), and the abovementioned resin component is blended so as to be within the abovementioned range with regard to the chain siloxane polymer component, properties such as curability, pressure-sensitive adhesive strength, storage elastic modulus, and the like, which are objects of the present invention, are suitably achieved. In particular, the mass ratio of component (B) to component (A) and component (A′) described later may be within a range of 1.1 to 3.0, and in order to achieve a desired pressure-sensitive adhesive strength and storage elastic modulus, may be 1.4 or more, 1.5 or more, or 2.0 or more, and is particularly preferably with a range of 1.4 to 3.0. In contrast, when the mass ratio of component (B) to component (A) and component (A′) described later is outside the aforementioned range, properties such as curability, pressure-sensitive adhesive strength, storage elastic modulus, and the like, which are objects of the present invention, may not be achieved even when other configurations are adjusted.

Component (C) is an organohydrogenpolysiloxane having two or more Si—H bonds in a molecule and is a crosslinking agent of the organopolysiloxane composition of the present invention. The molecular structure of component (C) is not particularly limited, and examples thereof include a straight chain, a partially branched straight chain, a branched chain, a cyclic, or an organopolysiloxane resin structure, and a straight chain, a partially branched straight chain, or an organopolysiloxane resin structure is preferable. The bonding position of silicon atom-bonded hydrogen atoms is not particularly limited, with examples thereof including molecular terminals, side chains, and both molecular terminals and side chains.

A content of the silicon atom-bonded hydrogen atoms is preferably from 0.1 to 2.0 mass % and more preferably from 0.5 to 1.7 mass %.

Examples of the organic groups bonded to silicon atoms include: methyl groups and other alkyl groups having 1 to 8 carbon atoms; phenyl groups and other aryl groups; aralkyl groups; and alkyl halide groups. 50 mol % or more of the total number thereof are preferably phenyl groups or alkyl group with 1 to 8 carbon atoms. From the perspective of ease of manufacture and compatibility with the preferred components (A) and (B) described above, the other organic groups are preferably methyl groups or phenyl groups.

Specific examples of component (C) include tris(dimethylhydrogensiloxy)methylsilane, tetra(dimethylhydrogensiloxy)silane, methylhydrogenpolysiloxanes capped at both terminals with trimethylsiloxy groups, copolymers of dimethylsiloxane and methylhydrogensiloxane capped at both terminals with trimethylsiloxy groups, copolymers of dimethylsiloxane and methylhydrogensiloxane capped at both terminals with dimethylhydrogensiloxy groups, cyclic methylhydrogen oligosiloxanes, cyclic copolymers of methylhydrogensiloxane and dimethylsiloxane, copolymers of methylhydrogensiloxane and diphenylsiloxane capped at both molecular terminals with trimethylsiloxy groups, copolymers of methylhydrogensiloxane, diphenylsiloxane and dimethylsiloxane capped at both molecular terminals with trimethylsiloxy groups, hydrolytic condensates of trimethylsilanes, copolymers consisting of (CH₃)₂HSiO_(1/2) units and SiO_(4/2) units, copolymers consisting of (CH₃)₂HSiO_(1/2) units, SiO_(4/2) units, and (C₆H₅)SiO_(3/2) units, copolymers consisting of (CH₃)₂HSiO_(1/2) units and CH₃SiO_(3/2) units, and mixtures of two or more types thereof.

Component (D) is a characteristic component of the present invention, and is an organic silicon compound having on average more than one alkenyl group in a molecule, which does not correspond to the component (A) and component (B) described above. These organic silicon compounds having an alkenyl group are usually reaction mixtures of alkenyl group-containing silanes and alkenyl group-containing silane-siloxanes used as independent adhesion imparting agents in curable siloxane compositions, and are different components from the polydialkylsiloxanes and other polyorganosiloxane components or organopolysiloxane resin components. The reaction mixture of the alkenyl group-containing silane-siloxane may contain heteroatoms such as nitrogen atoms and the like, and may be in a form of a reaction mixture containing a silatrane derivative or a carbasilatrane derivative having a structure in which the entire molecule is cyclized. These organic silicon compounds having alkenyl groups preferably have a function as an independent adhesion-imparting agent, and preferably have a low degree of polymerization and a low viscosity. The viscosity at 25° C. is preferably within a range of 1 to 500 mPa·s, and more preferably 1 to 350 mPa·s.

Preferred examples of component (D) include at least one type of organic silicon compound selected from a group consisting of:

(d1) an organic silicon compound having at least one silicon atom-bonded alkenyl group and at least one silicon atom-bonded alkoxy group in a molecule; (d2) an organic silicon compound having at least one silicon atom-bonded alkenyl group, at least one silicon atom-bonded alkoxy group, and at least one silicon-bonded epoxy-containing monovalent organic group in a molecule; (d3) a reaction mixture of a silane or siloxane having at least one silicon atom-bonded alkoxy group in a molecule and an organosiloxane having at least one silicon atom-bonded hydroxy group and at least one silicon atom-bonded alkenyl group in a molecule; and (d4) a reaction mixture of an organosilane having at least one silicon atom-bonded alkoxy group and at least one silicon atom-bonded epoxy-containing monovalent organic group in a molecule, an organosiloxane having at least one silicon atom-bonded hydroxy group or alkoxy group in a molecule, and an organosiloxane having at least one silicon atom-bonded alkenyl group in a molecule.

Herein, the organic silicon compound of components (d1) and (d2) are preferably silanes having one silicon atom, silane oligomers having two to three silicon atoms, and siloxanes having a branched unit. In particular, component (d2) is preferably an organic silicon compound having, in a molecule, a siloxane unit as expressed by EpSiO_(1.5) (where Ep is a silicon atom-bonded epoxy-containing monovalent organic group) and a siloxane unit as expressed by R¹R²SiO_(1.0) (where R¹ is an alkenyl group having 2 to 12 carbon atoms, and R¹ is an alkyl group having 1 to 12 carbon atoms), and may further have a silicon atom-bonded hydroxy group or alkoxy group in the molecule. Such a component (d2) has at least one epoxy-containing monomeric organic group in a molecule, and therefore can provide favorable adhesion to base materials, and thus is particularly preferable from the perspective of forming properties of a pressure-sensitive adhesive layer having excellent tensile adhesive strength.

The organic silicon compounds of components (d3) and (d4) are obtained as a reaction mixture of functional silane/siloxane, and is preferably a condensation reaction mixture in which each component is heated and mixed while stirring in the presence of a basic substance such as potassium hydroxide, sodium hydroxide, or the like.

Component (D) is particularly preferably (d4-1) a condensation reaction mixture of an organosilane having at least one silicon atom-bonded alkoxy group and at least one silicon atom-bonded epoxy-containing monovalent organic group in a molecule, an organosiloxane having at least one silicon atom-bonded hydroxy group or alkoxy group in a molecule, and an organosiloxane having at least one silicon atom-bonded alkenyl group in a molecule, which is an organic silicon compound having a siloxane unit as expressed by EpSiO_(1.5) (where Ep is a silicon atom-bonded epoxy-containing monovalent organic group) and a siloxane unit as expressed by R¹R²SiO_(1.0) (where R¹ is an alkenyl group having 2 to 12 carbon atoms, and R² is an alkyl group having 1 to 12 carbon atoms), in a molecule. Furthermore, a silicon-bonded hydroxy group or alkoxy group may be provided in the molecule.

Such a component (d4-1) has excellent handling workability, can impart favorable adhesiveness to various base materials due to having at least one epoxy-containing monomeric organic group in a molecule, in addition to rapidly curing by a hydrosilylation curing reaction without loss of viscoelastic properties such as shear storage elastic modulus G′ at room temperature or the like, and is particularly preferable from the perspective of forming properties of a pressure-sensitive adhesive layer having excellent tensile adhesive strength.

Examples of silicon atom-bonded epoxy-containing monovalent organic groups include epoxy-containing monovalent organic groups such as: 3-glycidoxypropyl groups, 4-glycidoxybutyl groups, and other glycidoxyalkyl groups; 2-(3,4-epoxycyclohexyl)ethyl groups, 3-(3,4-epoxycyclohexyl)propyl groups, and other (3,4-epoxycyclohexyl) alkyl groups; 4-oxiranylbutyl groups, 8-oxiranyloctyl groups, and other oxiranylalkyl groups; and the like. An alkenyl group having 2 to 12 carbon atoms is the same group as described above, and a vinyl group, an allyl group or a hexenyl group is preferred. Furthermore, an alkyl group having 1 to 12 carbon atoms is preferably industrially a methyl group.

[Sih/Vi Ratio]

The composition of the present invention is hydrosilylation reaction curable, where the substance amount of the silicon atom-bonded hydrogen atom (SiH) groups in component (C) is designed with regard to the sum of the substance amount of the alkenyl groups included in component (D) in addition to components (A) and (B). Thereby, the pressure-sensitive adhesive layer forming organopolysiloxane composition of the present invention has excellent curing properties.

For the amount of component (C) used in the composition of the present invention, the substance amount of silicon atom-bonded hydrogen atom (SiH) groups in component (C) relative to the sum of the amount (substance amount) of alkenyl groups in component (A), component (B), and component (D) in the composition, in other words, the molar ratio, must be 1.0 or more, is preferably within a range of 1.0 to 100, but may be within a range of 1.0 to 60, within a range of 1.5 to 55, or within a range of 2.0 to 50. In this range, the composition of the present invention exhibits favorable curing properties. On the other hand, if the aforementioned molar ratio is less than 1.0, curing defects may occur with the composition of the present invention. On the other hand, when the amount of the SiH groups exceeds the aforementioned upper limit, the amount of unreacted residual curing agent tends to increase, potentially having adverse effects on curing physical properties such as the brittleness of a cured product and the like, or potentially causing problems such as gas generation and the like.

On the other hand, the substance amount, in other words, the molar ratio, of the silicon atom-bonded hydrogen atom (SiH) groups in component (C) relative to the sum of the amount (substance amount) of the alkenyl groups in components (A) and (B) (in other words, an amount excluding the alkenyl groups in component (D)) in the composition can be designed to be 10 or more, or 20 or more, which is preferable. In particular, in order to improve close fitting properties with regard to a substrate of glass or the like of a pressure-sensitive adhesive layer obtained by curing the present composition, the substance amount of silicon atom-bonded hydrogen atom (SiH) groups in component (C) relative to the sum of the amount (substance amount) of alkenyl groups in component (A) and the amount (substance amount) of alkenyl groups in component (B) in the composition is particularly preferably designed to be within a range of 20 to 100 or a range of 22 to 90. By designing the amount of component (C) to be used within the aforementioned range, in addition to the conditions of the use of component (D) having a function as an adhesion promoter and the amount of component (C) used after taking into account the alkenyl group in component (D), the technical effect of improving close fitting properties to a substrate is more effectively achieved.

In other words, in the present invention, a most preferable amount of component (C) used is

an amount such that the ratio (molar ratio) of the substance amount of SiH groups in component (C) to the total substance amount of the alkenyl groups in components (A) and (B) is within a range of 20 to 100, and an amount such that the ratio (molar ratio) of the substance amount of SiH groups in component (C) to the total substance amount of the alkenyl groups in components (A), (B) and (D) is 2.0 to 80.

[Hydrosilylation Reaction Catalyst]

The organopolysiloxane composition according to the present invention contains (E) a hydrosilylation reaction catalyst. Examples of hydrosilylation reaction catalysts include platinum-based catalysts, rhodium-based catalysts, and palladium-based catalysts, with platinum-based catalysts being preferable in that they markedly accelerate the curing of the present composition. The platinum-based catalyst is preferably a platinum-alkenylsiloxane complex, and particularly preferably 1,3-divinyl-1,1,3,3-tetramethyldisiloxane due to the favorable stability of the platinum-alkenylsiloxane complex. As the catalyst for promoting the hydrosilylation reaction, a non-platinum based metal catalyst such as iron, ruthenium, iron/cobalt, or the like may be used.

In the present invention, the amount of the hydrosilylation reaction catalyst is not particularly limited. The amount of platinum-based metals may be, relative to the total amount of solid fractions in the composition, within a range of 0.1 to 200 ppm, may be within a range of 0.1 to 150 ppm or 0.1 to 100 ppm, and may also be within a range of 0.1 to 50 ppm. In practical use, the amount of the platinum metal excluding a ligand of the hydrosilylation reaction catalyst is preferably within the ranges described above. Note that the solid content is a component that forms the cured layer (primarily a main agent, an adhesion-imparting component, a crosslinking agent, a catalyst, and other non-volatile components) when the organopolysiloxane composition of the present invention is subjected to a curing reaction, and does not include volatile components such as solvents that volatilize at the time of heat curing.

When the amount of the platinum-based metal in the organopolysiloxane composition according to the present invention is 50 ppm or less (45 ppm or less, 35 ppm or less, 30 ppm or less, 25 ppm or less, or 20 ppm or less), discoloration or coloration of the transparent pressure-sensitive adhesive layer may be suppressed, particularly after curing or when heated or exposed to high-energy rays such as UV rays or the like. Meanwhile, from the perspective of the curability of the organopolysiloxane composition, the content of the platinum-based metal is no lower than 0.1 ppm, because when the content is lower than this lower limit, this may cause curing defects.

Component (F) is a curing retarder and is compounded in order to suppress a crosslinking reaction between the alkenyl groups in the composition and the SiH groups in component (C) so as to extend the usable life at ambient temperatures and enhance storage stability. Accordingly, in practical use, the component is a nearly essential component for the organopolysiloxane composition for forming a pressure-sensitive adhesive layer of the present invention.

Specific examples of component (E) include acetylenic compounds, ene-yne compounds, organic nitrogen compounds, organic phosphorus compounds, and oxime compounds. Specific examples include: alkyne alcohols such as 3-methyl-1-butyn-3-ol, 3,5-dimethyl-1-hexyn-3-ol, 3-methyl-1-pentyn-3-ol, 1-ethynyl-1-cyclohexanol, phenyl butynol, and the like; ene-yne compounds such as 3-methyl-3-penten-1-yne, 3,5-dimethyl-1-hexyn-3-yne, and the like; 2-ethynyl-4-methyl-2-pentene, methylalkenylcyclosiloxanes such as 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane, 1,3,5,7-tetramethyl-1,3,5,7-tetrahexenylcyclotetrasiloxane, and the like, as well as benzotriazoles. Note that a portion of component (E), which is a cyclic siloxane, overlaps with the component that functions as component (A).

From the perspective of the curing behavior of the composition, the organopolysiloxane composition for forming a pressure-sensitive adhesive layer of the present invention is preferably curable at 80 to 200° C., with an increase in viscosity of 1.5-fold after 8 hours at room temperature following the preparation of the composition. The suppression of thickening is important from the perspective of handleability, pot life, and characteristics after curing and contains a large excess of component (C), wherein, even if the amount of the platinum-based metal is optionally low, the curability can be ensured by curing at high temperatures of at least a certain temperature (80 to 200° C.). Note that such a composition can be achieved by selecting a suitable combination and compounded amounts of each of the components described above, the hydrosilylation catalyst, and component (E).

In addition to the aforementioned components described above, the organopolysiloxane composition according to the present invention may also contain an organic solvent as a solvent. The type and blending amount of the organic solvent is adjusted taking the coating workability and the like into consideration. Exemplary organic solvents include: aromatic hydrocarbon-based solvents such as toluene, xylene, and benzene; aliphatic hydrocarbon-based solvents such as heptane, hexane, octane, and isoparaffin; ester-based solvents such as ethyl acetate and isobutyl acetate; ether-based solvents such as diisopropyl ether and 1,4-dioxane; chlorinated aliphatic hydrocarbon-based solvents such as trichloroethylene, perchloroethylene, and methylene chloride; and solvent volatile oils, with two or more types capable of being combined in accordance with the wettability of the sheet-like substrate or the like. A compounded amount of the organic solvent is preferably an amount such that a mixture of components (A) to (C) can be uniformly applied to a sheet-like substrate surface. For example, the compounded amount may be from 5 to 300 parts by mass per total of 100 parts by mass of components (A), (B) and (C).

The organopolysiloxane composition of the present invention may optionally contain components other than the components described above to an extent that does not impair the technical effects of the present invention. Examples can include: antioxidants; light stabilizers; flame retardants; anti-static agents; and the like. Note that, in addition to these components, pigments, dyes, inorganic microparticles (reinforcing fillers, dielectric fillers, conductive fillers, thermally conductive fillers), and the like can be optionally blended.

[(A′) Chain Organopolysiloxane which does not Contain a Carbon-Carbon Double

Bond-Containing Reactive Group in a Molecule] The organopolysiloxane composition according to the present invention can optionally blend a non-reactive organopolysiloxane such as a polydimethylsiloxane, polydimethyldiphenylsiloxane, or the like that does not contain a carbon-carbon double bond-containing reactive group such as an alkenyl group, acryl group, methacryl group, or the like. As a result, it may be possible to improve the loss coefficient (tan δ), storage elastic modulus (G′), and loss modulus (G″) of the pressure-sensitive adhesive layer. For example, the loss coefficient of the pressure-sensitive adhesive layer can be increased using a polydimethylsiloxane having a hydroxyl group end and a polydimethylsiloxane or polydimethyldiphenylsiloxane having a trimethylsiloxy end, and such compositions are included within the scope of the present invention.

Herein, component (A′) is a chain organopolysiloxane that is not involved in the curing reaction by hydrosilylation, and the mass ratio of component (B) in the composition can affect the properties of the composition, such as the pressure-sensitive adhesive strength, storage elastic modulus, and the like. As described above, the mass ratio of component (B) to component (A) and component (A′) may be within a range of 1.1 to 3.0, and in order to achieve a desired pressure-sensitive adhesive strength and storage elastic modulus, may be 1.4 or more, 1.5 or more, or 2.0 or more, and is particularly preferably within a range of 1.4 to 3.0. Note that in order to suppress the storage elastic modulus of the composition, even if the mass ratio of component (B) to component (A) and component (A′) is designed to be high, the mass ratio of component (A) and component (A′) may be designed to be within a range of 100:0 to 60:40, 100:0 to 65:35, 90:10 to 65:35, 85:15 to 70:30, or the like.

The method of preparing the organopolysiloxane composition of the present invention is not particularly limited, and is performed by homogeneously mixing the respective components. A solvent may be added as necessary and the composition may be prepared by mixing at a temperature of from 0 to 200° C. using a known stirrer or kneader.

The organopolysiloxane composition of the present invention forms a coating film when applied to a substrate and forms a cured product by heating under temperature conditions of from 80 to 200° C. and preferably under temperature conditions of from 90 to 190° C. Examples of application methods include gravure coating, offset coating, offset gravure, roll coating, reverse roll coating, air knife coating, curtain coating, and comma coating. The coating amount can be designed at a desired thickness in accordance with the application such as a display device; for example, the thickness of the pressure-sensitive adhesive layer after curing may be from 1 to 1000 μm, from 5 to 900 μm, or from 10 to 800 μm; however, there is no limitation thereto.

[Range of Pressure Sensitive Adhesion and Adhesive Force]

The organopolysiloxane composition of the present invention is characterized in that a cured layer obtained by curing the composition by a hydrosilylation reaction is a pressure-sensitive adhesive. Because the pressure-sensitive adhesive layer according to the present invention has the abovementioned configuration and expresses sufficient adhesive force for practical use, a known silicone pressure-sensitive adhesive can be replaced and used as desired.

Specifically, a pressure-sensitive adhesive layer can be designed such that the pressure-sensitive adhesive force of the pressure-sensitive adhesive layer having a thickness of 50 μm obtained by curing the organopolysiloxane composition of the present invention, as measured at a tension rate of 300 mm/min using a 180° peeling test method in accordance with JIS Z 0237 for a polymethyl methacrylate sheet having a thickness of 2 mm, is within a range of 360 to 4000 gf/inch. A pressure-sensitive adhesive layer having a pressure-sensitive adhesive force within a range of 1300 to 3500 gf/inch is preferable. Note that the thickness (50 μm) described above is the thickness of the cured layer itself serving as a reference for objectively defining the adhesive force of the cured layer of the present invention. It goes without saying that the organopolysiloxane composition of the present invention is not limited to a thickness of 50 μm and may be used as a cured layer or a pressure-sensitive adhesive layer of any thickness.

[Storage Elastic Modulus and Other Mechanical Properties]

The pressure-sensitive adhesive layer forming organopolysiloxane composition of the present invention can be designed such that the shear storage elastic modulus G′ at 25° C. of the pressure-sensitive adhesive layer obtained by curing the composition is within a range of 0.005 to 20.00 MPa. The shear storage elastic modulus G′ may be within a range of 0.10 to 20.00 MPa, or may be within a range of 1.00 to 20.00 MPa. A range of 1.50 to 18.00 MPa is also preferably included within the scope of the present invention.

Furthermore, the composition of the present invention can be designed to have a stress at 500% strain at 25° C. of the pressure-sensitive adhesive layer obtained by curing the composition within a range of 0.005 MPa to 3 MPa, and may be 0.20 MPa to 3 MPa.

The pressure-sensitive adhesive layer-forming organopolysiloxane composition according to the present invention, which has a storage elastic modulus G′ at room temperature (25° C.) and tensile stress and having the aforementioned practical pressure-sensitive adhesive strength, is suitable as a member of a speaker, transducer, or other electronic apparatus or electrical device and suitable for applications in the field of advanced electronics materials and display elements such as smart devices and the like, in order to form an elastic pressure-sensitive adhesive member.

The storage elastic modulus (G′) of the pressure-sensitive adhesive layer according to the present invention can be measured via a known measurement method. For example, measurements can be performed using a storage elastic modulus (G′) MCR301 viscoelastic measurement device (available from Anton Paar). Using a disk shaped sample with a diameter of approximately 8 mm and a thickness of approximately 0.5 to 1 mm, the value can be obtained as a value at 25° C. by performing measurements within a range of −70° C. to 250° C. utilizing an 8 mm parallel plate at a frequency of 1 Hz, a strain of 0.1%, and a temperature increase rate of 3° C./minute.

The pressure-sensitive adhesive layer according to the present invention may have a storage elastic modulus G′ at 1.0 Hz at −20° C. which is no less than three-fold the storage elastic modulus G′ at 1.0 Hz at 25° C.

[Properties Relating to Transparency, Color Tone, or Coloration and Discoloration of the Pressure-Sensitive Adhesive Layer]

The organopolysiloxane composition of the present invention may be substantially transparent, translucent, or opaque, such that the transparency thereof can be designed in accordance with the application of the pressure-sensitive adhesive layer. Note that when it is visually transparent, or more objectively, when the value for air is 100%, the transmittance of light at a wavelength of 450 nm of the pressure-sensitive adhesive layer for a display device formed from a cured layer having a thickness of 100 μm is 80% or higher and suitably 90% or higher, and may be designed so as to be 95% or higher. In contrast, in the adhesion, and the like of the electrical or electronic part which does not require light transmittance, a semi-transparent to opaque pressure-sensitive adhesive layer may be used, with a filler component or additive which impairs colorability or light transmittance capable of being used depending on the required characteristics other than light transmittance.

The organopolysiloxane composition of the present invention can be designed such that a cured product is not colored, in addition to the aforementioned transparency, by optionally reducing the amount of the platinum-based metal in the cured layer. Furthermore, even when the cured layer of the present invention is exposed to high temperatures or high-energy beams such as UV rays or the like for an extended period of time, design can be such that the color tone thereof does not change significantly and the problem of yellowing, in particular, does not occur.

[Use as a Pressure-Sensitive Adhesive Layer]

The cured product of the present invention can, in particular, be used as a pressure-sensitive adhesive layer. In addition, in order to improve adhesion with the adherend, surface treatment such as primer treatment, corona treatment, etching treatment, or plasma treatment may be performed on the surface of the pressure-sensitive adhesive layer or the substrate. However, because the pressure-sensitive adhesive layer according to the present invention has excellent adhesion to a substrate of a display device and the like as described above, these steps may be added, as required, to further improve adhesion with the adherend, with a higher production efficiency capable of being achieved by eliminating these steps.

The curable organopolysiloxane composition of the present invention is cured by applying the composition to a release liner, then heating under the temperature conditions described above, and, after the release liner is peeled off and the composition is attached to a film-like substrate, a tape-like substrate, or a sheet-like substrate (hereinafter, referred to as a “film-like substrate”) or applied to a film-like substrate, curing by heating at the temperature conditions described above so as to form a pressure-sensitive adhesive layer on the surface of the substrate. A laminate provided with a cured layer, in particular, a film-like pressure-sensitive adhesive layer, obtained by curing the organopolysiloxane composition of the present invention on these film-like substrates may be used for adhesive tapes, adhesive bandages, low-temperature supports, transfer films, labels, emblems, and decorative or explanatory signs. Further, a cured layer obtained by curing the organopolysiloxane composition of the present invention may be used to assemble automobile parts, toys, electronic circuits, or keyboards. Alternatively, a cured layer formed by curing the organopolysiloxane composition of the present invention, particularly a film-like pressure-sensitive adhesive layer, may be used in the construction and use of a laminated touch screen or flat panel display. Note that an opposite surface of the film-like substrate from the pressure-sensitive adhesive layer surface may be subjected to surface treatments such as a treatment for scratch prevention, grime prevention, fingerprint adhesion prevention, anti-glare, anti-reflection, anti-static, or other treatment.

Exemplary types of substrates include paperboard, cardboard paper, clay-coated papers, polyolefin laminate papers, particularly polyethylene laminate papers, synthetic resin films and sheets, natural fiber woven materials, synthetic fiber woven materials, artificial leather woven materials, and metal foils.

The substrate is preferably a film-like or sheet-like substrate. The thickness thereof is not particularly limited and can be designed with a desired thickness in accordance with the application. Furthermore, in order to improve the adhesion between a supporting film and pressure-sensitive adhesive layer, a supporting film subjected to a primer treatment, corona treatment, etching treatment, or plasma treatment may be used. Furthermore, the opposite surface of the film-like substrate from the pressure-sensitive adhesive layer surface may be subjected to surface treatments such as a treatment for scratch prevention, grime prevention, fingerprint adhesion prevention, anti-glare, anti-reflection, anti-static, or other treatment.

As the application method to the substrate, gravure coating, offset coating, offset gravure, roll coating using an offset transfer roll coater, reverse roll coating, air knife coating, curtain coating using a curtain flow coater or the like, comma coating, Meyer bar, or other known methods used for the purpose of forming a cured layer may be used without limitation.

The coating amount can be designed at a desired thickness in accordance with the application such as a display device; for example, the thickness of the pressure-sensitive adhesive layer after curing may be from 1 to 1000 μm, from 5 to 900 μm, or from 10 to 800 μm; however, there is no limitation thereto.

The pressure-sensitive adhesive layer according to the present invention may be a single layer or a multilayer structure obtained by laminating two or more pressure-sensitive adhesive layers in accordance with the required characteristics. Multiple pressure-sensitive adhesive layer may be formed by bonding the pressure-sensitive adhesive films (which are formed film by film) thereto, or the step of applying and curing the pressure-sensitive adhesive layer-forming organopolysiloxane composition may be carried out multiple times on a film substrate (including a release layer) and the like.

The pressure-sensitive adhesive layer according to the present invention may serve as other functional layers selected from a dielectric layer, conductive layer, heat dissipation layer, insulating layer, reinforcing layer, and the like in addition to providing adhering or sticking functions between members.

When the cured layer obtained by curing the organopolysiloxane composition of the present invention is a pressure-sensitive adhesive layer, in particular, a pressure-sensitive adhesive layer, the cured layer is preferably treated as a laminate film that is peelably adhered to a film substrate provided with a release layer having a release-coating capability. The release layer may suitably be a release layer having a release coating capability, such as a silicone-based release agent, a fluorine-based release agent, an alkyd-based release agent, a fluorosilicone-based release agent, or the like, or a base material itself that has physically formed minute irregularities on the surface of the base material or that is difficult to adhere to the pressure-sensitive adhesive layer of the present invention. The use of a release layer obtained by curing a fluorosilicone-based release agent is preferred. Note that in the aforementioned laminated body, the release layer may be a different release layer, which is a first release layer and a second release layer having different types of release agents and different release forces configuring the release layer. The fluorosilicone-based release agent may be a curing reactive silicone composition containing one or more types of fluorine-containing groups selected from fluoroalkyl groups and perfluoropolyether groups.

The cured product obtained by curing the organopolysiloxane composition according to the present invention has both viscoelasticity and adhesive strength as described above, making it useful as a member of various types of electronic equipment or electrical devices as elastic adhesive members. In particular, it is useful as an electronic material, a member for a display device, or a member for a transducer (including sensors, speakers, actuators, and generators), with a suitable application for the cured product being a member for an electronic part or a display device. The cured product according to the present invention may be transparent or opaque, wherein, in particular, a film-shaped cured product, particularly a substantially transparent pressure-sensitive adhesive film, is suitable as a member for a display panel or a display, and is particularly useful in so-called touch panel applications in which a device, particularly an electronic device, can be operated by touching a screen with a fingertip or the like. Moreover, the opaque elastic adhesive layer is not required to have transparency, making it particularly useful for applications of film-like or sheet-like members used in sensors, speakers, actuators, and the like which require constant elasticity or flexibility in the adhesive layer itself.

In particular, the pressure-sensitive adhesive layer obtained by curing the organopolysiloxane composition according to the present invention is capable of achieving a pressure-sensitive adhesive characteristic equivalent to conventional silicone pressure-sensitive adhesive layers, and can improve adhesion to a substrate of a display device, and the like without causing problems due to poor curing or reduced curability.

[Member for Display Panel or Display]

A cured product obtained by curing the organopolysiloxane composition of the present invention can be used in the construction and use of a laminated touch screen or flat panel display, and the specific method of use thereof may be a known method of use of a pressure-sensitive adhesive layer (in particular, silicone PSA) without any particular limitation.

For example, a cured product obtained by curing the organopolysiloxane composition of the present invention can be used in the manufacturing of a display device such as a touch panel or the like as an optically transparent silicone-based pressure-sensitive adhesive film or a pressure-sensitive adhesive layer disclosed in Japanese Patent Application Publication (Translation of PCT Application) No. 2014-522436 A, Japanese Patent Application Publication (Translation of PCT Application) No. 2013-512326 A, or the like described above. In addition, a cured product obtained by curing the organopolysiloxane composition of the present invention may be used as an adhesive film for a polarizing plate used in the production of a display device such as a touch panel, or may be used as a pressure-sensitive adhesive layer used in bonding between a touch panel and a display module described in Japanese Patent Application Publication No. 2013-065009 A.

INDUSTRIAL APPLICABILITY

The application of the curing reactive organopolysiloxane composition of the present invention and a cured product obtained by curing the composition is not limited to those disclosed above, and the pressure-sensitive adhesive film provided with the cured product obtained by curing the composition can be used in various display devices for displaying characters, symbols and images. The surface shape of such a display device may be a curved shape or a bowed shape rather than a flat surface, with examples thereof including curved displays or curved transmission screens used in automobiles (including electric vehicles), aircraft, or the like in addition to various flat panel displays (FPDs). Further, these display devices can display icons for executing functions or programs on a screen or display, notification indicators of e-mail, programs, or the like, and operation buttons for various devices such as car navigation devices, audio devices, and air conditioning devices, with touch panel functions enabling input operations capable of being added by touching these icons, notification indicators, or operation buttons with a finger. Moreover, the cured product obtained by curing the composition has excellent adhesion and viscoelastic characteristics, enabling the use thereof as a film-like or sheet-like member which is a member for transducers such as a membrane for speakers (including a sensor, speaker, actuator, etc.), in addition to also being capable of being used as a sealing layer or adhesive layer used in a secondary battery, fuel cell, or solar cell module.

In addition, vehicle display devices having a curved display surface are disclosed in Japanese Patent Application Publication No. 2017-047767 A, Japanese Patent Application Publication No. 2014-182335 A, Japanese Patent Application Publication No. 2014-063064 A, Japanese Patent Application Publication No. 2013-233852 A and the like. However, the pressure-sensitive adhesive layer according to the present invention can be preferably applied or replaced as a portion or all of an adhesive layer or pressure-sensitive adhesive layer in which transparency is required in these documents.

EXAMPLES

Examples and comparative examples of the present invention are described hereinafter. Note that “cured” in each of the examples, comparative examples, and reference examples means that each composition has fully cured under the respective curing conditions.

(Preparation of Curing Reactive Organopolysiloxane Composition)

The curing reactive organopolysiloxane compositions illustrated in each of the examples, comparative examples, and reference examples were prepared using the components shown in Table 1. Note that all percentages in Table 1 refer to percentages by mass.

(Measurement of the Molecular Weight of the Organopolysiloxane Component)

Using gel permeation chromatography (GPC) available from Waters and tetrahydrofuran (THF) as a solvent, the weight average molecular weight (Mw) and number average molecular weight (Mn) of organopolysiloxane components such as organopolysiloxane resin were determined in terms of standard polystyrene.

(Measurement of the Content of Hydroxyl Groups (OH) in Organopolysiloxane Resin)

Using an ACP-300 ²⁹Si NMR spectrometer manufactured by Bruker provided with a glass-free probe, when the chemical shift of the tetramethylsilane was set to 0 ppm, the molar content was obtained from the presence ratio of Si(OH)O_(2/3) units appearing at −93 to −103.5 ppm to all silicons, then further converted into the mass % of the hydroxyl groups (OH) in the organopolysiloxane resin. Note that hydrolyzable functional groups other than hydroxyl groups were not included in the organopolysiloxane resin in the following examples.

(Adhesive Force Measurement)

Each composition was applied to a PET film (available from Toray Co., Ltd., product name: Lumirror (registered trademark) S10, thickness: 50 μm) such that the thickness after curing was 50 μm, after which it was cured for 3 minutes at 150° C. After being left to stand for one day, the sample was cut to a width of 20 mm and the adhesive layer surface was affixed to a PMMA plate (manufactured by Paltec, ACRYLITE L001, 50×120×2 mm) using a roller to form a test piece. Regarding the test piece using the PMMA plate, the adhesive force (measurement at a width of 20 mm converted to the display unit gf/inch) was measured at a tensile speed of 300 mm/min using the 180° peeling test method in accordance with JIS Z 0237, using an RTC-1210 tensile tester manufactured by Orientec Co., Ltd.

(Dynamic Viscoelasticity: Storage Elastic Modulus G′ at 25° C.)

Each composition was applied to a release liner coated via fluorosilicone release coating such that the thickness after curing was approximately 100 μm, then cured at 150° C. for three minutes. Five or more of the pressure-sensitive adhesive films were overlapped so as to obtain a film sample, both surfaces of which were sandwiched between release liners having a thickness of 500 μm or more. The film was cut to a diameter of 8 mm and adhered to the parallel plate probe of a dynamic viscoelastic device (MCR301 available from Anoton Paar) in order to determine the storage elastic modulus G′. The measurement conditions were within a range of −70° C. to 250° C., the measurements were carried out at a frequency of 1 Hz and a temperature increase rate of 3° C./minute, the loss coefficient, storage elastic modulus G′ and loss modulus G″ were measured, and the storage elastic modulus G′ at 25° C. was recorded (units: MPa).

(Tensile Test)

A film sample having a thickness of 500 μm or more, obtained in the same manner as the abovementioned dynamic viscoelasticity test sample with both surfaces sandwiched between release liners, was cut to a width of approximately 5 mm and a length of approximately 70 mm, then the release liners were peeled off while applying baby powder to the pressure-sensitive adhesive surface to form a tensile test sample. The tensile test was carried out using Autograph AGS-X available from Shimadzu Corporation to grab approximately 25 mm above or below the sample at a speed of 300 mm/minute. Stress and strain were determined from the exact sample width and thickness of each sample and the distance between the crossheads, and the stress at 500% strain was recorded (units: MPa).

(Tensile Adhesive Strength)

Each composition was applied to a release liner coated with a fluorosilicone release coating such that the thickness after curing is approximately 200 μm, and then cured at 150° C. for 3 minutes, and another release liner was adhered to a pressure-sensitive adhesive surface. The sample was cut into 5 mm squares, the release liner was peeled off, and a pressure-sensitive adhesive layer was adhered between two PMMA plates (ACRYLITE L001 manufactured by Paltek Corporation, 75×25×2 mm) combined in a crisscross pattern to form a test piece. Using an Autograph AGS-X manufactured by Shimadzu Corporation, a jig gripping each of the upper and lower PMMA plates was used to vertically peel off the pressure-sensitive adhesive surface, and a tensile test was conducted at a rate of 100 mm/min to measure the stress at the time of rupture.

The materials of the curing reactive organopolysiloxane compositions are shown in Table 1. Note that the viscosity or plasticity of each component was measured at room temperature using the following methods.

[Viscosity]

The viscosity (mPa·s) is a value measured using a rotary viscometer conforming to JIS K7117-1, and the kinematic viscosity (mm²/s) is a value measured with an Ubbelohde viscometer conforming to JIS Z8803.

[Plasticity]

The plasticity was expressed as a value measured in accordance with the method prescribed in JIS K 6249 (the thickness when a 1 kgf load was applied for 3 minutes to a 4.2 g spherical sample at 25° C. was read up to 1/100 mm, and this value was multiplied by 100).

TABLE 1 Components of the curing reactive organopolysiloxane compositions Component Name Component Component a1 Vinyl-functional polydimethylsiloxane, Gum-like (plasticity: 152), vinyl content: 0.013 mass % Component a2 Vinyl-functional polydimethylsiloxane, Gum-like (plasticity: 160), vinyl content: 0.065 mass % Component b1 MQ silicone resin consisting of (CH₃)₃ SiO_(1/2) units, SiO_(4/2) units, and hydroxyl groups, Mw: 6500, OH content: 4.5 mole % (1.0 mass %), xylene solution (solid content: 63.8%) Component b2 MQ silicone resin containing (CH₃)₃SiO_(1/2) units, SiO_(4/2) units, and hydroxyl groups, Mw: 3300, OH content: 3.5 mol % (0.8 mass %), xylene solution (solid fraction: 75.5%) Component c1 Methylhydrogenpolysiloxane capped at both terminals of the molecular chain with trimethylsiloxy groups, viscosity: 20 mm²/s, SiH content: 1.59% Component d Weight average molecular weight (Mw) of 940 as measured by GPC in terms of standard polystyrene Average compositional formula: Alkenyl group-containing organic silicon compound (adhesion promoter) as expressed by [(CH₃)₂SiO_(2/2)]_(0.45)[(CH₂═CH)CH₃SiO_(2/2)]_(0.24)[CH₂(O)CHCH₂O(CH₂)₃SiO_(3/2)]_(0.31)[CH₃O_(1/2)]_(0.50), with a vinyl amount of 5.53% by mass* Component e Platinum-based hydrosilylation reaction catalyst containing 0.62 mass % platinum Component f 1-ethynyl-1-cyclohexanol, 20% toluene solution *A condensation mixture in the presence of potassium hydroxide of 3-glycidoxypropyltrimethoxysilane, silanol-terminated dimethylpolysiloxane, and 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasiloxane

Example 1

36.4 parts by weight of the vinyl functional polydimethylsiloxane of component a2, 99.4 parts by weight of the MQ silicone resin of component b1, 30.9 parts by weight of toluene, 1.30 parts by weight of the methylhydrogenpolysiloxane of component c1, 0.491 parts by weight of the curing retarder 20% solution of component e, and 2.00 parts by weight of an alkenyl group-containing organic silicon compound (adhesion promoter) of component d were sufficiently mixed at room temperature, and then 0.355 parts by weight of the platinum-based hydrosilylation reaction catalyst of component e was added to the mixture to obtain a curing reactive organopolysiloxane composition. The molar ratio of the SiH groups in component c1 to the amount of the alkenyl groups in component a2 (SiH/Vi ratio) was 28.7, the molar ratio of the SiH groups in component c1 to the sum of the alkenyl groups in component a2 and the alkenyl groups in component d (SiH/Vi ratio) was 5.00, and the amount of platinum metal to solid fractions was 22 ppm. The composition was cured via the aforementioned method, and then the pressure-sensitive adhesion, stress strain, pressure-sensitive adhesive strength on a PMMA plate, and tensile adhesive strength were measured by methods indicated above. The evaluation results and the like are shown in Table 2.

Example 2

32.3 parts by weight of the vinyl functional polydimethylsiloxane of component a2, 100.8 parts by weight of the MQ silicone resin of component b1, 4.3 parts by weight of the MQ silicone resin of component b2, 29.3 parts by weight of toluene, 1.56 parts by weight of the methylhydrogenpolysiloxane of component c1, 0.491 parts by weight of the curing retarder 20% solution of component e, and 2.00 parts by weight of an alkenyl group-containing organic silicon compound (adhesion promoter) of component d were sufficiently mixed at room temperature, and then 0.355 parts by weight of the platinum-based hydrosilylation reaction catalyst of component e was added to the mixture to obtain a curing reactive organopolysiloxane composition. The molar ratio of the SiH groups in component c1 to the amount of the alkenyl groups in component a2 (SiH/Vi ratio) was 31.7, the molar ratio of the SiH groups in component c2 to the sum of the alkenyl groups in component a2 and the alkenyl groups in component d (SiH/Vi ratio) was 5.00, and the amount of platinum metal to solid fractions was 22 ppm. The composition was cured via the aforementioned method, and then the pressure-sensitive adhesion, stress strain, pressure-sensitive adhesive strength on a PMMA plate, and tensile adhesive strength were measured by methods indicated above. The evaluation results and the like are shown in Table 2.

Example 3

32.3 parts by weight of the vinyl functional polydimethylsiloxane of component a2, 100.8 parts by weight of the MQ silicone resin of component b1, 4.3 parts by weight of the MQ silicone resin of component b2, 29.3 parts by weight of toluene, 3.74 parts by weight of the methylhydrogenpolysiloxane of component c1, 0.491 parts by weight of the curing retarder 20% solution of component e, and 2.00 parts by weight of an alkenyl group-containing organic silicon compound (adhesion promoter) of component d were sufficiently mixed at room temperature, and then 0.355 parts by weight of the platinum-based hydrosilylation reaction catalyst of component e was added to the mixture to obtain a curing reactive organopolysiloxane composition. The molar ratio of the SiH groups in component c1 to the amount of the alkenyl groups in component a2 (SiH/Vi ratio) was 76.2, the molar ratio of the SiH groups in component c1 to the sum of the alkenyl groups in component a2 and the alkenyl groups in component d (SiH/Vi ratio) was 12.0, and the amount of platinum metal to solid fractions was 22 ppm. The composition was cured via the aforementioned method, and then the pressure-sensitive adhesion, stress strain, pressure-sensitive adhesive strength on a PMMA plate, and tensile adhesive strength were measured by methods indicated above. The evaluation results and the like are shown in Table 2.

Example 4

36.4 parts by weight of the vinyl functional polydimethylsiloxane of component a1, 99.4 parts by weight of the MQ silicone resin of component b1, 86.4 parts by weight of toluene, 0.349 parts by weight of the methylhydrogenpolysiloxane of component c1, 0.409 parts by weight of the curing retarder 20% solution of component e, and 1.00 parts by weight of an alkenyl group-containing organic silicon compound (adhesion promoter) of component d were sufficiently mixed at room temperature, and then 0.355 parts by weight of the platinum-based hydrosilylation reaction catalyst of component f was added to the mixture to obtain a curing reactive organopolysiloxane composition. The molar ratio of the SiH groups in component c1 to the amount of the alkenyl groups in component a1 (SiH/Vi ratio) was 31.6, the molar ratio of the SiH groups in component c1 to the sum of the alkenyl groups in component a1 and the alkenyl groups in component d (SiH/Vi ratio) was 2.43, and the amount of platinum metal to solid fractions was 22 ppm. The composition was cured via the aforementioned method, and then the pressure-sensitive adhesion, stress strain, pressure-sensitive adhesive strength on a PMMA plate, and tensile adhesive strength were measured by methods indicated above. The evaluation results and the like are shown in Table 2.

(Comparative Example 1)

36.4 parts by weight of the vinyl functional polydimethylsiloxane of component a2, 99.4 parts by weight of the MQ silicone resin of component b1, 86.4 parts by weight of toluene, 0.298 parts by weight of the methylhydrogenpolysiloxane of component c1, 0.491 parts by weight of the curing retarder 20% solution of component e, and 2.00 parts by weight of an alkenyl group-containing organic silicon compound (adhesion promoter) of component d were sufficiently mixed at room temperature, and then 0.355 parts by weight of the platinum-based hydrosilylation reaction catalyst of component e was added to the mixture to obtain a curing reactive organopolysiloxane composition. The molar ratio of the SiH groups in component c1 to the amount of the alkenyl groups in component a2 (SiHVi ratio) was 5.40, the molar ratio of the SiH groups in component c1 to the sum of the amount of alkenyl groups in component a2 and the alkenyl groups in component d (SiH/Vi ratio) was 0.94, and the amount of platinum metal to solid fractions was 22 ppm. An attempt was made to cure the composition by the method described above, but the composition did not cure.

(Comparative Example 2)

32.3 parts by weight of the vinyl functional polydimethylsiloxane of component a2, 100.8 parts by weight of the MQ silicone resin of component b1, 4.3 parts by weight of the MQ silicone resin of component b2, 84.9 parts by weight of toluene, 0.266 parts by weight of the methylhydrogenpolysiloxane of component c1, 0.491 parts by weight of the curing retarder 20% solution of component e, and 2.00 parts by weight of an alkenyl group-containing organic silicon compound (adhesion promoter) of component d were sufficiently mixed at room temperature, and then 0.355 parts by weight of the platinum-based hydrosilylation reaction catalyst of component e was added to the mixture to obtain a curing reactive organopolysiloxane composition. The molar ratio of the SiH groups in component c2 to the amount of the alkenyl groups in component a2 (SiH/Vi ratio) was 5.40, the molar ratio of the SiH groups in component c1 to the sum of the alkenyl groups in component a2 and the alkenyl groups in component d (SiH/Vi ratio) was 0.85, and the amount of platinum metal to solid fractions was 22 ppm. An attempt was made to cure the composition by the method described above, but the composition did not cure.

(Comparative Example 3) #254

36.4 parts by weight of the vinyl functional polydimethylsiloxane of component a2, 99.4 parts by weight of the MQ silicone resin of component b1, 30.9 parts by weight of toluene, 0.298 parts by weight of the methylhydrogenpolysiloxane of component c1, and 0.491 parts by weight of the curing retarder 20% solution of component f were sufficiently mixed at room temperature, and then 0.355 parts by weight of the platinum-based hydrosilylation reaction catalyst of component e was added to the mixture to obtain a curing reactive organopolysiloxane composition. The molar ratio (SiH/Vi ratio) of SiH groups in component c1 to the amount of alkenyl groups in component a2 was 5.40, while the amount of the platinum metal to the solid fraction was 22 ppm. The composition was cured via the aforementioned method, and then the pressure-sensitive adhesion, stress strain, pressure-sensitive adhesive strength on a PMMA plate, and tensile adhesive strength were measured by methods indicated above. The evaluation results and the like are shown in Table 2.

(Comparative Example 4)

32.3 parts by weight of the vinyl functional polydimethylsiloxane of component a2, 100.8 parts by weight of the MQ silicone resin of component b1, 4.3 parts by weight of the MQ silicone resin of component b2, 84.9 parts by weight of toluene, 0.266 parts by weight of the methylhydrogenpolysiloxane of component c1, and 0.491 parts by weight of the curing retarder 20% solution of component f were sufficiently mixed at room temperature, and then 0.355 parts by weight of the platinum-based hydrosilylation reaction catalyst of component e was added to the mixture to obtain a curing reactive organopolysiloxane composition. The molar ratio (SIH/Vi ratio) of SiH groups in component c1 to the amount of alkenyl groups in component a2 was 5.40, while the amount of the platinum metal to the solid fraction was 22 ppm. The composition was cured via the aforementioned method, and then the pressure-sensitive adhesion, stress strain, pressure-sensitive adhesive strength on a PMMA plate, and tensile adhesive strength were measured by methods indicated above. The evaluation results and the like are shown in Table 2.

(Comparative Example 5)

36.4 parts by weight of the vinyl functional polydimethylsiloxane of component a1, 99.4 parts by weight of the MQ silicone resin of component b1, 86.4 parts by weight of toluene, 0.349 parts by weight of the methylhydrogenpolysiloxane of component c1, 0.409 parts by weight of the curing retarder 20% solution of component e, and 3.00 parts by weight of an alkenyl group-containing organic silicon compound (adhesion promoter) of component d were sufficiently mixed at room temperature, and then 0.355 parts by weight of the platinum-based hydrosilylation reaction catalyst of component e was added to the mixture to obtain a curing reactive organopolysiloxane composition. The molar ratio of the SiH groups in component c1 to the amount of the alkenyl groups in component a1 (SiH/Vi ratio) was 31.6, the molar ratio of the SiH groups in component c1 to the sum of the alkenyl groups in component a1 and the alkenyl groups in component d (SiH/Vi ratio) was 0.87, and the amount of platinum metal to solid fractions was 22 ppm. An attempt was made to cure the composition by the method described above, but the composition did not cure.

TABLE 2 SiH/Vi of Storage Pressure- the entire elastic Stress Tensile sensitive b/a b1/b2 composition modulus at 500% adhesive adhesive Mass Mass (component a + G′ (MPa) strain strength strength ratio ratio component d) at 25° C. (MPa) (MPa) (gf/inch) Example 1 1.75 100/0 5.00 2.09 1.70 2.26 1600 Example 2 2.10  95.2/4.8 5.00 7.84 1.71 2.89 1960 Example 3 2.10  95.2/4.8 12.0 9.04 1.76 3.10 1990 Example 4 1.75 100/0 2.43 1.91  0.203 — 2230 Comparative 1.75 100/0 0.94 Uncured Example 1 Comparative 2.10  95.2/4.8 0.85 Uncured Example 2 Comparative 1.75 100/0 5.40 2.62 1.45 2.03 1600 Example 3 Comparative 2.10  95.2/4.8 5.40 6.37 1.82 2.46 2310 Example 4 Comparative 1.75 100/0 0.87 Uncured Example 5

SUMMARY

As shown in Table 2, the pressure-sensitive adhesive layer forming organopolysiloxane compositions of Examples 1 to 4 have sufficient curability and could be designed in a wide range with a storage elastic modulus G′ at 25° C. of 1.0 MPa or more, and could be designed with a stress at 500% strain of 0.20 MPa or more, and pressure-sensitive adhesive strength to a PMMA of 1300 gf/inch or more. As a result, it was possible to obtain the organopolysiloxane compositions for forming a pressure-sensitive adhesive layer with excellent curing reactivity, practically sufficient pressure-sensitive adhesive strength, and a wide range of designable viscoelastic properties such as storage elastic modulus and the like.

On the other hand, in Comparative Examples 1, 2 and 5, in which the SiH/Vi ratio is outside the range of the present invention, no curing occurred even when component d was used.

In contrast, Example 1 and Comparative Example 3, and Example 2 and Comparative Example 4 have the same composition except for component d. However, when comparing the tensile adhesive strength of the Comparative Examples and the Examples, the Examples in which component d is added indicated a higher value. In other words, even for compositions having similar SiH/Vi ratios with regard to compositions using component d, the adhesive properties of each of the compositions in the Comparative Examples cannot be sufficiently improved. 

1. An organopolysiloxane composition for forming a pressure-sensitive adhesive layer, the composition comprising: (A) a chain or cyclic organopolysiloxane having on average more than one alkenyl group in a molecule; (B) an organopolysiloxane resin in which the sum of contents of hydroxyl groups and hydrolyzable groups relative to all silicon atoms in a molecule is 9 mol % or less; (C) an organohydrogenpolysiloxane having at least two Si—H bonds in a molecule; (D) an organic silicon compound having on average more than one alkenyl group in a molecule, and excluding components corresponding to components (A) and (B); and (E) an effective amount of a hydrosilylation reaction catalyst; and optionally, (A′) a chain organopolysiloxane not containing a reactive group containing a carbon-carbon double bond in a molecule; wherein an amount of component (C) is an amount such that a ratio (molar ratio) of the substance amount of SiH groups in component (C) to the total substance amount of alkenyl groups in components (A), (B) and (D) is 1.0 or more.
 2. The organopolysiloxane composition for forming a pressure-sensitive adhesive layer according to claim 1, wherein component (D) is at least one type of an organic silicon compound selected from a group consisting of: (d1) an organic silicon compound having at least one silicon atom-bonded alkenyl group and at least one silicon atom-bonded alkoxy group in a molecule; (d2) an organic silicon compound having at least one silicon atom-bonded alkenyl group, at least one silicon atom-bonded alkoxy group, and at least one silicon-bonded epoxy-containing monovalent organic group in a molecule; (d3) a reaction mixture of a silane or siloxane having at least one silicon atom-bonded alkoxy group in a molecule and an organosiloxane having at least one silicon atom-bonded hydroxy group and at least one silicon atom-bonded alkenyl group in a molecule; and (d4) a reaction mixture of an organosilane having at least one silicon atom-bonded alkoxy group and at least one silicon atom-bonded epoxy-containing monovalent organic group in a molecule, an organosiloxane having at least one silicon atom-bonded hydroxy group in a molecule, and an organosiloxane having at least one silicon atom-bonded alkenyl group in a molecule.
 3. The organopolysiloxane composition for forming a pressure-sensitive adhesive layer according to claim 1, wherein component (D) is: (d4-1) a condensation reaction mixture of an organosilane having at least one silicon atom-bonded alkoxy group and at least one silicon atom-bonded epoxy-containing monovalent organic group in a molecule, an organosiloxane having at least one silicon atom-bonded hydroxy group or alkoxy group in a molecule, and an organosiloxane having at least one silicon atom-bonded alkenyl group in a molecule, which is an organic silicon compound having a siloxane unit as expressed by EpSiO_(1.5) where Ep is a silicon atom-bonded epoxy-containing monovalent organic group and a siloxane unit as expressed by R¹R²SiO_(1.0) where R¹ is an alkenyl group having 2 to 12 carbon atoms, and R² is an alkyl group having 1 to 12 carbon atoms), in a molecule.
 4. The organopolysiloxane composition for forming a pressure-sensitive adhesive layer according to claim 1, wherein component (D) is an adhesion promoter.
 5. The organopolysiloxane composition for forming a pressure-sensitive adhesive layer according to claim 1, wherein a mass ratio of component (B) to the sum of component (A) and component (A′) is within a range of 0.9 to 3.0, and wherein a pressure-sensitive adhesive layer obtained by curing the composition has a shear storage elastic modulus G′ at 25° C. of 0.005 MPa to 20 MPa, a stress at 500% strain at 25° C. of 0.005 MPa to 3 MPa, and a pressure-sensitive adhesive force of 360 gf/inch to 4000 gf/inch as measured at a tension rate of 300 mm/min using a 180° peeling test method in accordance with JIS Z 0237 for a polymethyl methacrylate sheet having a thickness of 2 mm, when a thickness of the pressure-sensitive adhesive layer is 50 μm.
 6. The organopolysiloxane composition for forming a pressure-sensitive adhesive layer according to claim 1, wherein an amount of component (C) is a substance amount such that the ratio (molar ratio) of the amount of SiH groups in component (C) to the total substance amount of the alkenyl groups in components (A) and (B) is within a range of 20 to
 100. 7. The organopolysiloxane composition for forming a pressure-sensitive adhesive layer according to claim 1, wherein an amount of component (C) is an amount such that the ratio (molar ratio) of the substance amount of SiH groups in component (C) to the total substance amount of the alkenyl groups in components (A), (B) and (D) is within a range of 2.0 to
 50. 8. The organopolysiloxane composition for forming a pressure-sensitive adhesive layer according to claim 1, wherein component (B) is an organopolysiloxane resin mixture containing the following component (b1) and component (b2) at a mass ratio of 1:99 to 99:1: (b1) an organopolysiloxane resin, where the total content of hydroxyl groups and hydrolyzable groups relative to all silicon atoms in a molecule is 9 mol % or less, and a weight average molecular weight (Mw) measured in terms of standard polystyrene by gel permeation chromatography (GPC) is 4500 or more; and (b2) an organopolysiloxane resin, where the total content of hydroxyl groups and hydrolyzable groups relative to all silicon atoms in a molecule is 9 mol % or less, and a weight average molecular weight (Mw) measured in terms of standard polystyrene by gel permeation chromatography (GPC) is less than
 4500. 9. The organopolysiloxane composition for forming a pressure-sensitive adhesive layer according to claim 1, wherein: at least a portion of component (A) is (A1) a raw rubber-like organopolysiloxane containing an alkenyl group having a viscosity of 100,000 mPa·s or more at 25° C. or having a plasticity within a range of 50 to 200 as measured in accordance with a method as specified in JIS K6249, and is a chain organopolysiloxane where a content of vinyl (CH₂═CH) portions of the alkenyl groups is within a range of 0.005 to 0.400 mass %; an organopolysiloxane resin mixture for component (B) is an organopolysiloxane resin mixture containing a R₃SiO_(1/2) unit (M unit) and an SiO_(4/2) unit (Q unit), where R is a monovalent organic group and 90 mol % or more of R is an alkyl group having 1 to 6 carbon atoms or a phenyl group; and an amount of component (E) is an amount such that a platinum-based metal in a solid fraction of the composition is within a range of 0.1 to 200 ppm.
 10. The organopolysiloxane composition for forming a pressure-sensitive adhesive layer according to claim 1, wherein a mass ratio of component (B) to the sum of component (A) and component (A′) is within a range of 1.4 to 3.0, and wherein a pressure-sensitive adhesive layer obtained by curing the composition has a shear storage elastic modulus G′ at 25° C. of 1.0 MPa to 20 MPa, a stress at 500% strain at 25° C. of 0.20 MPa to 3 MPa, and a pressure-sensitive adhesive force of 1300 gf/inch to 3500 gf/inch as measured at a tension rate of 300 mm/min using a 180° peeling test method in accordance with JIS Z 0237 for a polymethyl methacrylate sheet having a thickness of 2 mm, when a thickness of the pressure-sensitive adhesive layer is 50 μm.
 11. A pressure-sensitive adhesive layer obtained by curing the organopolysiloxane composition for forming a pressure-sensitive adhesive layer according to claim
 1. 12. A laminated body, comprising a pressure-sensitive adhesive layer obtained by curing the organopolysiloxane composition for forming a pressure-sensitive adhesive layer according to claim 1 on a film-like substrate.
 13. The laminated body according to claim 12, wherein a release layer for the pressure-sensitive adhesive layer is provided on one or two or more film-like substrates.
 14. An elastic pressure-sensitive adhesive member obtained by curing the organopolysiloxane composition for forming a pressure-sensitive adhesive layer according to claim
 1. 15. An electronic apparatus or electrical device, comprising the elastic pressure-sensitive adhesive member according to claim
 14. 16. A speaker, comprising the elastic pressure-sensitive adhesive member according to claim
 14. 